Apparatuses are known for continuously manufacturing charcoal in a rotary furnace in which a temperature of about 650.degree. C. to 700.degree. C. is maintained in a carbonization zone. Ordinary charcoal is obtained at the outlet from the furnace having a maximum carbon content of about 85% and a volatile matter content of about 10% of the total weight.
Some metallurgical or chemical industries require charcoal having a higher carbon content, e.g. a carbon content which is greater than 95% of the total weight of charcoal plus volatile matter.
If such carbon-rich charcoal is made from coal, then the resulting product contains inorganic impurities (sulfur, phosphorus, traces of metal, etc. . . .), making it unsuitable for some uses. However charcoal made from wood does not contain such impurities, and is well suited to the requirements of certain industries, in particular for manufacturing activated charcoal for the chemical and pharmaceutical industries.
Carbon-rich charcoal has already been manufactured by discontinuous methods.
An object of the present invention is to provide means for manufacturing charcoal continuously in a rotary furnace and having a carbon content greater than 95% of the total weight of carbon plus volatile matter, with this result being achieved by adjusting the operating parameters of the furnace and certain details of the construction of the rotary furnace.
The term "charcoal" is used herein to designate charcoal of vegetable origin obtained by carbonization of wood or any other vegetable material.
The object of the invention is achieved by a method of carbonizing wood or vegetable matter in a rotary furnace in which the temperature of the carbonization zone lies in the range 900.degree. C. to 1000.degree. C. and the transit time through the furnace lies in the range 45 minutes to 60 minutes.
Preferably, the fragments of wood or vegetable matter inserted into the furnace have a particle size of less than 5 mm and a water content of less than 10% of total weight.
Advantageously, combustible gases due to pyrolysis are collected from the inlet of the furnace and a fraction thereof are reinjected to the outlet of the furnace so that the recycling of said gases equalizes the temperature of the gaseous atmosphere inside the furnace.
The invention provides apparatuses of the type comprising a rotary furnace in which vegetable matter is carbonized in a reducing atmosphere, and from which charcoal and combustible gases due to the pyrolysis of the vegetable matter are collected.
Apparatus of the invention further includes a hot gas generator fitted with a burner which is fed with a fraction of the pyrolysis gases leaving the furnace, and a drier which is heated by the hot gases produced by said generator and which serves to dry green wood and moist vegetable matter prior to delivering them to the rotary furnace for carbonization.
A rotary furnace of the invention is fitted with an axial burner, which burner is a two-fuel burner burning both a fraction of the pyrolysis gases leaving said furnace and a second fuel which arrives via a second duct, which second duct includes a motor driven regulator valve driven by a motor which simultaneously drives a second regulator valve disposed on the duct feeding the burner with combustion air, which motor is automatically controlled by a temperature regulation system so as to maintain inside the furnace both a reducing atmosphere and a temperature lying in the range 900.degree. C. to 1000.degree. C.
The effect of the present invention is continuous manufacture of charcoal with a carbon content greater than 95% of the total weight of carbon plus volatile matter.
This result is achieved by a special choice of operating parameters, in particular of a temperature in the carbonization zone lying in the range 900.degree. C. to 1000.degree. C., of a transit time through the furnace lying in the range 45 minutes to 60 minutes, and of a particle size of the vegetable matter which is less than 5 mm.